Green’s Dictionary of Slang

(US) smart, aware, knowledgeable.

1905		H. Green Actors’ Boarding House (1906) 316: Was it me fault the old geezer can’t get Joe Hep to which shell the pea’s under?
1921		P. & T. Casey Gay-cat 208: I tries to explain that I meant on’y I was Jerry, Johnny Hep, wise, yuh know.
1940		D. Maurer Big Con 300: joe hep or hep. Smart, or ‘wise’ to what is happening. Probably ironically so called from one Joe Hep, the proprietor of a saloon in Chicago where grifters had their headquarters.